1. Field of the Invention
The present invention relates to techniques useful in the microbial industry. More specifically, the present invention relates to a method for producing L-lysine or L-arginine by fermentation, and a microorganism used in the production method.
2. Background Art
Amino acids such as L-lysine, L-glutamic acid, L-threonine, L-leucine, L-isoleucine, L-valine and L-phenylalanine are industrially produced by fermentation using microorganisms that belong to the genus Brevibacterium (Corynebacterium), Bacillus, Escherichia, Streptomyces, Pseudomonas, Arthrobacter, Serratia, Penicillium, Candida or the like. Strains isolated from nature, or artificial mutants thereof, have been used to improve the productivity of these microorganisms. Moreover, various techniques have been disclosed for increasing the L-amino acid producing abilities, such as recombinant DNA techniques to enhance L-amino acid biosynthetic enzymes.
Production of L-amino acids has been considerably increased by breeding of microorganisms such as those mentioned above with improved production methods. However, in order to respond to further increases in demand in future, development of methods which provide more efficient production of L-amino acids at lower cost are clearly still necessary, and therefore, still represent a need in the art.
Methanol is a known fermentation raw material which is available in large amounts at a low cost. Methods for producing L-amino acids by fermentation using methanol are known, and include methods using microorganisms that belong to the genus Achromobacter or Pseudomonas (Japanese Patent Publication (Kokoku) No. 45-25273), Protaminobacter (Japanese Patent Laid-open (Kokai) No. 49-125590), Protaminobacter or Methanomonas (Japanese Patent Laid-open No. 50-25790), Microcyclus (Japanese Patent Laid-open No. 52-18886), Methylobacillus (Japanese Patent Laid-open No. 4-91793), Bacillus (Japanese translation of PCT international application Patent (Kohyo) No. 3-505284) (WO90/12105) and so forth. The inventors of the present invention have developed methods for producing L-amino acids by breeding Methylophilus bacteria using artificial mutagenesis and recombinant DNA techniques (WO 00/61723).
In recent years, proteins have been identified that have a function of specifically secreting an L-amino acid to the outside a cell of microorganism, as well as genes which encode these proteins. In particular, Vrljic et al. have identified a gene involved in secretion of L-lysine derived from Corynebacterium glutamicum R127 to the outside of a cell (Vrljic M., Sahm H., Eggeling L., Molecular Microbiology 22:815-826 (1996)). This gene was designated as lysE, and it was reported that L-lysine producing ability of Corynebacterium bacteria could be improved by enhancing the expression of this gene in Corynebacterium bacteria (WO97/23597). The gene lysE is known to secrete not only L-lysine, but also L-arginine (Bellmann A., Vrljic M., Patek M., Sahm H., Kramer R., Eggeling L. Microbiology, 147:1765-1774 (2001)). It is also known that production of some L-amino acids can be improved by increasing expression amounts of amino acid secreting proteins in Escherichia coli (Japanese Patent Laid-open No. 2000-189180). For example, it is reported that production of cystine, cysteine, and so forth can be improved by enhancing the expression of ORF306 gene in Escherichia coli (EP885962).
However, there have been no reports to date suggesting that the amino acid secretion process is involved either positively or negatively in amino acid production by fermentation of methanol using a methanol-assimilating bacterium. There have also been no reports suggesting an amino acid secretion gene that can provide secretion activity in a methanol-assimilating bacterium.